The present invention relates to a mass transfer apparatus and method. More particularly, the present invention relates to an improved and more efficient mixing vessel and impeller arrangement to be employed in liquid aeration processes. The invention is useful, for example, for use in waste treatment plants for introducing oxygen and/or oxygen containing gas into waste water. The invention is also useful in various other mass transfer processes.
In mass transfer processes such as waste treatment and bio-reactions, it is common to carry out these processes in a stirred vessel in which gas, such as oxygen or an oxygen containing gas, is introduced into a liquid containing a solid phase and/or micro-organisms therein. These aforementioned processes are oftentimes utilized by municipalities and industry to treat waste wherein the object of the process is to introduce oxygen to the liquid so that the micro-organisms contained therein can use this oxygen to digest the waste. The gas is commonly introduced by means of sparge pipes into a tank containing liquid and/or use of a surface aerator such as an impeller.
Surface aerators function both to stir and agitate the liquid while imparting energy onto the liquid, causing turbulence on the liquid surface along with causing the liquid to splash. As a result of the splashing and the turbulence of the liquid, the liquid is contacted by air and the liquid is thereby aerated.
During waste treatment process, the gas is initially introduced to the liquid, and after a period of time, the micro-organisms will have effected sufficient reaction for clear and/or treated liquid to be run off, possibly after a settling stage.
One disadvantage with these processes is that they are very inefficient. The length of time required to effect the reaction can be as long as 24 hours. This time period, combined with the fact that these waste treatment processes are oftentimes carried out continuously year round, provide a process that is very inefficient in terms of both time consumption and energy consumption.
In addition, oftentimes the impeller or surface aerator of waste treatment apparatuses are operated at such high power levels that the turbulence and the spray of the liquid is so great that liquid impacts or hits the mixing vessel walls at high velocities. As a result of these high velocity impacts, the liquid spray loses some of its kinetic energy, imparting some of its energy on the walls instead of the liquid surface. As a result of this loss of energy, less liquid surface turbulence occurs causing less aerating of the liquid. In addition, when the surface aerator is being operated at the previously mentioned high power levels, it tends to pump and spray water so fast that it essentially xe2x80x9cstarvesxe2x80x9d itself because the return liquid is not provided to the surface aerator as quickly as the aerator is pumping and discharging the liquid.
Also, as more energy is inputted into the surface of the liquid, the liquid located near the surface becomes increasingly more aerated, causing the density of the surface liquid to become significantly reduced. As a result, the low density liquid imparts a greater load on the impeller of the mixing system as the system attempts to pull the bubbles and aerated liquid into the depths of the mixing vessel. This greater load reduces the liquid flow of the mixing vessel, reducing mass transfer.
The aforementioned reduction in mass transfer also negatively affects the bottom velocities of the mixing vessel, which are utilized to suspend solids in the tank and are instrumental to obtaining a thoroughly, agitated mixture.
Current mixing apparatuses attempt to address the above described occurrences include employing a second mixing impeller. Oftentimes the second impeller is positioned near the bottom of the mixing vessel to assist in drawing the low density surface liquid downward and to increase bottom velocities. This arrangement oftentimes does not work, because it creates two flow patterns within the vessel and cuts down the magnitude of the liquid flow in the bottom of the mixing vessel.
Accordingly, it is desirable to provide an improved aeration apparatus for effectuating the energy efficient dispersement or transfer gas or other fluids into a liquid or liquid suspension in mixing systems. It is also desirable to provide efficient mass transfer while not compromising the bottom velocities of the mixing vessel or causing the liquid flow pattern within the vessel to be disrupted.
The foregoing needs are met, at least in part, by the present invention where, in one aspect, an improved mixing vessel for mixing and aerating a liquid or liquid suspension is provided. The improved mixing vessel includes at least one side wall and a bottom wall. The mixing apparatus also has a first reflector attached to the at least one side wall. The reflector is positioned at a first angle to the side wall.
In accordance with another aspect of the present invention, an improved mixing apparatus is provided having a vessel and a shaft. The mixing apparatus additionally includes a first impeller having a first diameter attached to the shaft and a second impeller having a second diameter attached to the shaft. The first impeller and second impeller are positioned a distance. This distance is equal to between approximately 0.20 to approximately 0.75 of the first diameter.
In accordance with another aspect of the present invention, an improved mixing vessel for mixing and aerating a liquid or liquid suspension is provided. The improved mixing vessel has at least one side wall and a bottom wall along with at least one reflector. The reflector is attached to the at least on side wall and/or bottom wall and the reflector is positioned at an angle to the bottom wall.
In accordance with still another aspect of the present invention, a method for aerating a liquid is provided, comprising agitating a liquid to form a spray in a vessel having at least one side and a bottom wherein the spray contacts the side; and deflecting the spray from the at least one side at an angle in the direction of the bottom of the vessel.
In accordance with yet another aspect of the present invention, an improved mixing apparatus is provided having means for containing a liquid or liquid suspension having at least one side and a bottom. The mixing apparatus also includes a means for agitating a liquid to form a spray that contacts the at least one side of the containing means along with a means for deflecting the spray from the at least one side at an angle in the direction of the bottom of the containing means.
There has thus been outlined, rather broadly, several features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described below and which will form the subject matter of the claims appended hereto.
In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting.
As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.